Pseudorabies virus (PRV) is a herpesvirus which can infect most domestic animals to cause clinical symptoms ranging from vomiting, diarrhea, fever, respiratory problems, neurological disorders, abortion, and culminating, generally, in death to the host animal.
Pseudorabies is known as Aujeszky's disease, mad itch and bulbar paralysis. When PRV infects pigs, a serious economic loss is incurred by the farmer. Very young pigs die whereas older pigs get sick and lose weight. Pregnant sows will abort when infected with PRV. Thus, an effective program for the eradication of PRV in swine is urgently needed.
Herpesviruses are among the most complex of animal viruses, coding for the synthesis of at least 50 virus specific proteins. Among the most immunologically reactive proteins of herpesviruses are the glycoproteins found in virion membranes and in the membranes of infected cells. The literature on pseudorabies glycoproteins (Ben-Porat, T., and Kaplan, A. S. Virology 41, 265-273, 1970; Kaplan, A. S., and Ben-Porat, T., Proc. Natl. Acad. Sci. USA, 66, 799-806, 1970) indicates that there are at least four viral glycoproteins in infected cells and virons.
Glycoproteins excreted into the medium have been reported for several herpesviruses, including herpes simplex virus (Kaplan, A. S., Erickson, J. S., and Ben-Porat, T., Prog. Med. Virol. 21, 1-12, 1975); herpes saimiri virus (Randall, R. E., and Honess, R. W., J. Gen. Virol. 51, 445-449, 1980); Marek's disease virus (Van Zaane, D., Brinkhof, J. M., Westenbrink, F., and Gielkens, A. L., Virology 121, 116-132, 1981); and pseudorabies virus (Erickson, J. S., and Kaplan, A. S., Virology 55, 94-102, 1973). In each of these cases except PRV, the excreted glycoprotein(s) is reported to be a subset of the virion glycoproteins. The publication by Ben-Porat and Kaplan, 1970, discloses that the PRV excreted glycoprotein is distinct from virion glycoproteins. This glycoprotein is known as 3a in the prior art (see Erickson and Kaplan, 1973, supra) and is referred to hereinafter as glycoprotein gX. Glycoprotein gX has the following characteristics when harvested from PRV-infected cells:
(1) it is the predominant protein in the culture medium of PRV infected animal cells in culture;
(2) it is a glycoprotein;
(3) it has a molecular weight of about 95 kilodaltons by standard SDS polyacrylamide gel electrophoresis (DATD cross-linked gel);
(4) it is a sulfated protein;
(5) it is soluble in about 1% perchloric acid;
(6) it is immunogenic in standard laboratory mice; and,
(7) it raises an immune response in the animal host which response is protective against a lethal challenge by a virulent strain of PRV.
We have isolated and mapped from the unique small region of pseudorabies virus (PRV) genome the gene encoding the PRV excreted glycoprotein gX and cloned said gene to express a fragment of the protein.